1. Field of the Invention
The present invention relates to optical communication network management and services. Specifically, this invention relates to simultaneously applying a low-level subcarrier modulation signal to multiple high-bit-rate modulated optical data signals propagating through the same fiber or similar path. A slow response-time summing amplifier is utilized at a reception point in the optical communication network to sum individual subcarrier components and thereby create a high signal-to-noise ratio of subcarrier modulation signals within the subcarrier channel of the communication network.
2. Related Art
A typical communication network, serving to transport information among a number of locations, consists of various physical sites, called nodes, interconnected by information conduits, called "links." Each link serves to carry information from one site to another site. Individual sites contain equipment for combining, separating, transforming, conditioning, and/or routing data.
Optical networks that include a plurality of optical transmission lines or links permit high bandwidth data communications, and may be used in telephone and other data network systems. High speed data can be modulated on light waves which are transmitted through the optical network. The optical transmission line, connecting an optical transmitter and receiver, can propagate many light wave signals of different frequencies simultaneously. One type of multi-frequency (or multi-wavelength) communication is found in wavelength-division-multiplexed (WDM) networks. See, e.g., U.S. Pat. No. 4,821,255, issued Apr. 11, 1989 to Kobrinski, incorporated herein by reference in its entirety. Thus, fiber optic communications links carry vast amounts of information among distant sites to accomplish data, voice and image connectivity over a large geographical area.
Optical networks carry high-data rate traffic supporting an ever-increasing variety and range of interconnected data networks, lower-level networks, distributed systems, consumer communication products and services, and remote units. As the proliferation and diversity of network elements and signals becomes greater, network management becomes even more critical.
Thus, a primary concern for network providers is accurately tracking the flow of data signals that traverse the communication network through various nodes, switching sites, and links. One method of tracking information without affecting the high data rate modulation signal is by providing ancillary network data as a rider on a high data rate modulated optical signal, as disclosed in the present inventor's related applications entitled "Method and System for Detecting LMink Failure in All Optical Communication Network," Ser. No. 08/582,845, and "All Optical Network with Low Level Subcarrier for Ancillary Data," Ser. No. 08/673,651. This subcarrier modulated signal can be used to monitor the status of the data signals, without having to alter the high data rate modulation signal itself.
For example, a low-level subcarrier signal can have a peak-to-peak intensity modulation that is a fraction of that of the high data rate modulated signal. A single period of the low-level subcarrier signal is then spread over thousands of high-rate bits and is readily separable by inexpensive optical detectors.
However, a problem can arise in detecting the subcarrier modulation signal as a result of a poor signal-to-noise ratio (SNR). Typical sources of noise within a communication network include: signal-spontaneous beat noise created from the subcarrier signal and the amplified stimulated emission (ASE) of optical amplifiers and regenerators; the spontaneous-spontaneous beat noise created by the ASE itself; shot noise created from the subcarrier signal and ASE; and thermal noise. For a discussion on the types of noise found in optical communication systems, see Murakami, et al., "A Remote Supervisory System Based on Subcarrier Overmodulation for Submarine Optical Amplifier Systems," Jour. of Lightwave Tech., Vol. 14, No. 5, 671-677 (May 1996), which is incorporated by reference in its entirety herein. Because the subcarrier modulation signal must have a low amplitude as compared to the high data rate modulation signal (i.e., low enough to not interfere with reliable reception of the high-bit-rate signal), detection of the subcarrier signal is especially vulnerable to noise problems leading to a low SNR.